Operating circuits for electro-magnetic devices



Oct. 19, 1965 B. J. WARMAN ETAL 3,213,332

OPERATING CIRCUITS FOR ELECTROMAGNETIC DEVICES 2 P? W F n 3 6 I? 'Cd INVENTORS a aaur/ap JAM'S mum/a {9, T #40040 JAMES ST/Rl/NG ATTORNEY S Patented Oct. 19, 1965 3,213,332 UPERATHNG CIRCUETS FUR ELECTRO- MAGNETHC DEVMIES Bloomfield James Warman, Charlton, London, and Harold James Stirling, Orpington, England, assignors to Associated Electrical Industries (Wooiwich), Limited, London, England, a British company Filed May 20, 1958, Ser. No. 736,567 Claims priority, application Great Britain, June 13, 1957, 18,699/ 57 Claims. (Cl. 317-1555) This invention relates to pulse-responsive operating circuits for electromagnetic devices, for instance relays, and has as its object the provision of a circuit which permits such a device to be operated (that is, picked up or released in the case of a relay) in response to electrical pulses the duration of which is shorter than the operating time of the device.

According to the present invention an electromagnetic device having an operating winding connected in an output circuit of an electronic device, such as a thermionic valve or transistor, for control by input pulses applied to said electronic device, has a further winding inductively coupled with the operating winding and connected to provide, on change of energisation of the operating winding, consequent on reception of an input pulse, a regenerative feedback to an input circuit for the electronic device whereby effectively to lengthen the duration of the input pulse as received by this latter device and applied to the operating winding. The change of energisation referred to may be a change from a de-energised condition to an energised condition or vice versa, dependent, in the case of a relay for instance, or whether an input pulse tends to pick up the relay or release it. If desired, a contact controlled by the electromagnetic device may be connected in a maintaining circuit for the latter so as to maintain an operated condition thereof after the end of a lenghtened pulse from which such condition resulted.

The invention has an important application in so-called core circuitry requiring operation of an electromagnetic device in response to impulse output from a wound magnetic core of ferrite or other material exhibiting an approximately rectangular hysteresis loop when subjected to a cycle of magnetisation, the duration of such output being usually very short, in the region of two to five microseconds for instance. The invention may also be applied to the operation of a relay or other electromagnetic device from a multi-cathode, cold cathode electronic discharge tube, such as a dekatron, in response to its discharge momentarily investing a particular cathode thereof during a scanning action by which the cathodes are invested in turn. Another important application is to relay operation via multiplex channels; application of the invention to this latter purpose enables a number of relatively slow-operating relay circuits to be scanned at high speed, for instance by means of a multi-cathode tube as referred to above, by multiplex pulses which merely initiate the operation of the relays, leaving them to complete their operation by virtue of the regenerative feedback action.

In order that the invention may be more fully understood reference will now be made to the accompanying drawings in which, by way of example:

FIGS. 1, 2 and 3 are circuit diagrams illustrating the application of the invention to relay operation from a ferrite core; and

FIG. 4 is a circuit diagram illustrating another application of the invention and also a different manner of applying an input operating pulse to the relay.

In each of FIGS. 1, 2 and 3 a relay R is to be operated by an output pulse from a ferrite core F. In FIG. 1 the relay R has an operating winding RWl connected in the emitter-collector circuit of a transistor T the base of which is connected to one side of an output winding FWl on the ferrite core F. The other side of this winding FWl is connected through a second winding RW2 on the relay R to a make-before-break change-over contact set RCa which, being controlled by the relay R in accordance as it is picked up or released, extends this connection either through a resistor 11 to a source of negative bias potential -B for the transistor T or through another resistor r2 to a source of positive bias potential +B. The two windings RWl and RW2 on the relay R are inductively coupled with each other and are connected in their respective circuits in such sense that, on initiation of current flow in the operating winding RWl as a result of the transistor T being rendered conductive by a negative-going pulse applied to its base, the winding RW2 produces a negative signal at the transistor base; in other words, there is an inductive regenerative feedback action from the emitter-collector circuit of the transistor T to its base circuit by way of the inductive coupling between the relay windings RWl and RW2.

The ferrite core F has two input windings FWZ and FW3 to one of which, FW2, are applied negative-going pulses p1 displaced in time with respect to positive-going pulses p2 applied to the other winding FW3, each input pulse being effective to cause the core F to turn over, that is, to change the existing polarity of the core magnetisation to the opposite polarity in accordance with the now well-known principles of ferrite core circuitry. Consider as a starting point a condition in which the transistor T is non-conductive and the relay R is therefore de-energised so that its change-over contact set RCa applies the positive bias =+B to the transistor base, this ensuring that the transistor T is held cut off. On application to the ferrite core F of an input pulse, say p1, which has the effect of turning over the core in the direction to generate in winding FWl an output pulse of polarity such as to drive the transistor base negative, the transistor T is brought into conduction and current flows through the operating winding RWl of the relay R. The regenerative feedback action induced through the relay windings RWl, RW2 maintains the conduction of the transistor T during the rise of magnetic flux in the relay R, even though the output pulse from the winding FWI of the ferrite core F may have terminated in the meantime. When the relay R picks up at the end of its inherent time lag, it actuates the change-over contact set RCa so that the negative bias potential B is now applied to the transistor base instead of the positive potential +B. This results in the transistor T being held conductive until when the core is turned over in the reverse direction by a subsequent (p2) input pulse, the resultant positive output pulse applied to the transistor base from winding FWI causes the transistor T to be cut off. The slow decay of current through the feedback winding RW2 of the relay R tends to maintain the positive potential of the tran sistor base and therefore maintains the transistor T in its nonconductive state sufficiently long for the relay R to release and its change-over contacts RCa to re-apply the positive bias -l-B to the base, the non-conductive state of the transistor T being thereafter maintained by this latter bias.

The circuit of FIG. 2 is similar to that of FIG. 1 (corresponding circuit elements being similarly identified) eX- cept that the relay feedback winding RW2 is no longer connected to a change-over contact set of the relay. Instead, the path extending from the base of the transistor T through the output coil FWl of the ferrite core F and the relay feedback winding RW2, extends on the other side of this latter winding to a source of positive bias potential +B through a resistor r3 and to a source of negative bias potential -B through a resistor rd in series with a make contact R!) of the relay R. In the released condition of the relay R the transistor T is held non-conductive by the positive bias +B. Consequent on an output pulse of appropriate polarity from the winding FWl of the ferrite core F, the transistor T is rendered conductive as previously explained and the relay R is picked up at the end of its inherent time lag, the feedback action, similar to that obtained With the circuit of FIG. 1, being effective until then to maintain the conductive condition of the transistor T. Once the relay R has picked up and closed its make contact RCb, the previously existing positive bias at the transistor base is changed to a negative bias by the potential dividing action of the two resistors r3 and r4, which are now connected in series, through the closed make contact RCb, between the positive and negative bias sources +3 and B. The resistance values are appropriately chosen to give the requisite change in the bias applied to the transistor base in order to maintain the transistor T conductive.

The circuit of FIG. 3 is similar to that of FIG. 2 except that the make contact RCb in FIG. 2 is omitted from the connection to the negative bias potential B and a break contact RCc of the relay R is included instead in the connection to the positive bias potential -|-B. With the transistor T non-conductive and the relay R de-energised, the closed break contact RCc connects resistors 1'3 and rd in series between the two potential sources B and +3, the values of the resistors being chosen such that in this condition the transistor base receives a positive potential maintaining the non-conductive state of the transistor T. After the relay has been picked up in the same manner as before, the positive bias +B is disconnected at the break contact RCc and the negative potential B maintains the then conductive state of the transistor; otherwise the operation is the same as for FIG. 2.

It will be appreciated, in regard to the circuits of FIGS. 2 and 3, that release of the relay R on reverse operation will restore the initial bias conditions on the transistor base, as it does in the first example.

Regarding the values of the resistors used in the foregoing examples, it may be noted that the values chosen therefor must be such that the potentials applied through them to the base of the transistor T are sufficient to maintain the transistor either conductive or non-conductive as may be required at any particular time, but not so large as to prevent an output pulse from the ferrite core F from triggering the transistor T to its opposite state and thereby initiating the regenerative action.

The relay employed may be of a standard type having at least two windings of which one can be used as the operating winding RWI and the other as the feedback winding RW2: for instance a relay such as that employed for feeding bridge circuits in an automatic telephone exchange may be suitable.

A relay of the foregoing standard type may in fact have three inductively coupled windings of which one may have a fewer number of winding turns than the others. FIG. 4- illustrates an application of the invention in which an operating input pulse for a three-winding relay R is applied to one winding, RW3, of the relay while the regenerative action introduced according to the invention is effected by the other two windings RWI and R'WZ in conjunction with transistor T. With the transistor T initially non-conductive, an input pulse applied to winding RW3 of relay R induces in winding R'WZ, by virtue of the inductive coupling between these windings, a pulse which is of such polarity as to bring the transistor base negative and thereby cause the transistor to conduct, this conductive condition being maintained, during the rise of the flux in the relay R, by a regenerative action afforded by windings RWll and R'WZ as before. In this instance, by way of a modification over the circuits of FIGS. 1 and 2, the transistor T is restored to its nonconductive condition once the relay R has been picked up and this condition of the relay is maintained by the establishment for its winding RWl of a maintaining circuit including make contact RCd of the relay and a release contact Rel. This latter contact may be controlled in any desired manner to open the maintaining circuit and thus release the relay R at an appropriate time subsequent to its operation.

It is envisaged that, instead of there being the output winding of only one ferrite core in the transistor base circuit, other arrangements in which the output windings of more than one core are included in the transistor base circuit might be devised and might have useful application in simplifying relay type circuit designs by enabling relay operation to be permitted depending upon the prior occurrence of certain external circuit actions.

In the application of the invention illustrated in FIG. 4, the operating input pulses for the relay R are obtained from a multi-cathode, cold cathode discharge tube D. This tube is shown conventionally as comprising ten cathodes 1, 8, 9, (I, a common anode a, and two guide electrode terminals 21 and e2 to which guide electrodes (not shown), disposed between the cathodes for controlling the transfer of the discharge from one cathode to the next, are connected in well-known manner. Driving pulses p3 are applied to the guide electrode terminals el and 02 through resistors 1'5 and r6, the presence of a capacitor c1 having the effect of delaying the application of these pulses to the terminal 62 as is required for the operation of the tube D. Cathode resistors r7 provide that when the tube discharge invests any particular cathode, its potential rises in a positive-going sense by reason of the voltage drop then produced across the cathode resistor for that particular cathode. The circuit of FIG. 4 provides for the picking up of the relay R when the discharge in the tube D, driven from cathode to cathode by the pulses p3, invests a particular cathode (cathode 8 as shown) when certain external circuit conditions obtain, the relay R being then picked up even if the discharge remains only momentarily on the cathode concerned. To this end the input pulse to the relay R is taken from cathode 8 of the tube D by way of capacitor 02 and coincidence gate G. When the conditions referred to obtain, the gate G has a priming signal applied to it via terminal g, with the result that when the tube discharge next invests cathode 8 the consequent rise in potential of this cathode is passed as an input pulse via capacitor and gate G to the relay R which picks up in response thereto in the mnaner previously described. By applying the input pulses to the winding RW3 of the relay R rather than to winding R'WZ as in FIGS. 13, D.C. isolation is ob tained between the relay circuit and the discharge tube circuit. Moreover, if the winding RW3 has fewer turns than RW2, a step-up transformer action is obtained by which the input pulses are magnified before application to the base of transistor T.

The operation of a relay from a multi-cathode tube as in the circuit of FIG. 4 may be required in various circumstances in connection, for instance, with certain forms of electronic telephone or telecommunication systems. A possible application which has already been mentioned would be in respect of a multiplex system in which a number of relay circuits corresponding to that of the relay R in FIG. 4 are required to be rapidly scanned under control of hte multiplex pulses: to this end the multiplex pulses could be applied as drive pulses to the tube D and the several relays connected to receive respective input pulses derived from different cathodes of the tube in a manner similar to that for relay R.

What we claim is:

1. A pulse responsive circuit comprising an operable electromagnetic device having an operating winding and a feedback winding inductively coupled with each other,

together with an electronic device operable by applied input pulses between a conductive state and a substantially non-conductive state and having an output circuit including said operating winding, an input circuit including said feedback winding, said feedback winding being effective, on change of energisation of the operating winding consequent on application of an input pulse to the electronic device, to provide a regenerative feedback action which in effect lengthens the duration of the input pulse, and a maintaining circuit including a contact which is controlled by the electromagnetic device and functions to change a bias condition on the electronic device from a first condition which tends to maintain the electronic device in one of its said states of conduction but permits it to be changed to the other state by an applied input pulse, to a second condition which tends to maintain said other state of conduction.

2. A pulse responsive circuit as claimed in claim 1 including a further winding by means of which input pulses can be inductively injected into the input circuit of the electronic device.

3. A pulse responsive circuit as claimed in claim 2 wherein said further winding is constituted by an output winding of a wound magnetic core of material exhibiting an approximately rectangular hysteresis loop characteristic.

4. A pulse responsive circuit comprising a transistor having an emitter-collector circuit and a base circuit, an electromagnetic device having an operating winding connected in the transistor emitter-collector circuit and a feedback winding connected in the transistor base circuit, means including a further winding in the transistor base circuit for inductively injecting into this latter circuit input pulses effective to operate the transistor between states of conduction and substantially non-conduction of its emitter-collector circuit, said feedback winding being effective, on change of energisation of the operating winding consequent upon an input pulse, to provide a regenerative feedback action which in effect lengthens the duration of the input pulse as it affects the base circuit, and a maintaining contact which is operable in the transistor base circuit by the electromagnetic device and functions to change a bias condition on the transistor from a first condition which tends to maintain the transistor in one of its said states but permits it to be changed by an input pulse to the other state, to a second condition which tends to maintain said other state of the transistor.

5. A pulse responsive circuit as claimed in claim 4 wherein said further winding is constituted by an output winding of a wound magnetic core of material having an approximately rectangular hysteresis loop characteristic.

References Cited by the Examiner UNITED STATES PATENTS 2,685,665 8/54 Price 317-449 2,761,998 9/56 Chen 317-'149 2,787,742 4/57 Fransen.

2,801,374 7/57 Svala 317148.5 X

SAMUEL BERNSTEIN, Primary Examiner. 

1. A PULSE RESPONSIVE CIRCUIT COMPRISING AN OPERABLE ELECTROMAGNETIC DEVICE HAVING AN OPERATING WINDING AND A FEEDBACK WINDING INDUCTIVELY COUPLED WITH EACH OTHER, TOGETHER WITH AN ELECTRONIC DEVICE OPERABLE BY APPLIED INPUT PULSES BETWEEN A CONDUCTIVE STATE AND A SUBSTANTIALLY NON-CONDUCTIVE STATE AND HAVING AN OUTPUT CIRCUIT INCLUDING SAID OPERATING WINDING, AN INPUT CIRCUIT INCLUDING SASID FEEDBACK WINDING, SAID FEEDBACK WINDING BEING EFFECTIVE, ON CHANGE OF ENERGISATION OF THE OPERATING WINDING CONSEQUENT ON APPLICATION OF AN INPUT PULSE TO THE ELECTRONIC DEVICE, TO PROVIDE A REGENERATIVE FEEDBACK ACTION WHICH IN EFFECT LENGTHENS THE DURATION OF THE INPUT PULSE, AND A MAINTAING CIRCUIT INCLUDING A CONTACT WHICH IS CONTROLLED BY THE ELECTROMAGNETIC DEVICE AND FUNCTIONS TO CHANGE A BIAS CONDITION ON THE ELECTRONIC DEVICE FROM A FIRST CONDITION WHICH TENDS TO MAINTAIN THE ELECTRONIC DEVICE IN ONE OF ITS SAID STATES OF CONDUCTION BUT PERMITS IT TO BE CHANGED TO THE OTHER STATE BY AN APPLIED INPUT PULSE, TO A SECOND CONDITION WHICH TENDS TO MAINTAIN SAID OTHER STATE OF CONDUCTION. 